1. Field of the Invention
The invention relates to a drive train connecting an engine and a motor in a vehicle, and more specifically to a hybrid vehicle drive train having a motor integrated with an automatic transmission or a manual transmission into a single unit.
2. Description of the Related Art
Japanese Patent Application No. HEI 9-215270, Japanese Patent Application No. HEI 9-23846 and Japanese Patent Application No. HEI 5-30605 all disclose parallel type hybrid vehicle drive trains. This type of hybrid vehicle drive train is provided with an engine and a motor/generator in a transmission. Driving forces of the engine and the motor/generator are transmitted to the transmission during start and acceleration of the vehicle. The motor/generator also functions as a generator to assist the engine brake effect when driving down a hill and also regenerates braking energy, thereby improving gas mileage and reducing the amount of discharged exhaust gas.
In the drive trains disclosed by HEI 9-215270 and HEI 9-238436, a motor/generator is arranged between an engine and a transmission. Therefore, the axial dimension of the drive train is increased by the axial length of the motor/generator, and the size of the drive train is thereby increased.
In the drive train disclosed by HEI 9-215270, a rotor of the motor/generator is rotatably supported by a fixed member, e.g., a housing or the like. In this case, the fixed member needs to extend to nearby the rotor. Therefore, the axial dimension of the drive train is increased, and the size of the drive train is likewise increased.
Another method directly supports the rotor by the crankshaft of the engine without the fixed member, in which case the crankshaft is rotatably supported by plural supports, and the mass of the rotor connecting to the crankshaft is mainly supported by that support which is nearest to the rotor support. The nearest supporting portion and the center of gravity of the rotor are axially offset. Therefore, if the rotor is arranged on the crankshaft in an overhanging state, the mass of the rotor must be supported over a longer distance than the supporting portion. As a result, the crankshaft and the plural supports therefor are overstressed, and the engine is also adversely affected.
If the mass of the rotor must be supported over a longer distance than provided by the supporting portion mentioned above, the rotor tends to rotate eccentrically. Further, the rotor is directly supported by the crankshaft of the engine. Therefore, when the crankshaft rotates eccentrically due to the explosion vibrations of the engine, the rotor tends to also rotate eccentrically. To avoid contacting the rotor with a stator when the rotor rotates eccentrically, a greater gap between the rotor and the stator must be provided. As a result, the size of the motor/generator increases, and the efficiency of the motor/generator decreases.
In the drive train disclosed by HEI 5-30605, a motor/generator is arranged so as to bypass between a pump impeller and a turbine runner of a torque converter. A rotor of the motor/generator is supported by the torque converter cover. In this structure, when the converter cover is deformed by charge pressure and/or centrifugal pressure, the accuracy of centering of the rotor decreases.
In view of the above problems associated with the prior art, an object of the invention is to provide a hybrid vehicle drive train which minimizes the axial dimension of the drive train and the size of the drive train.
To achieve the foregoing object, the invention provides a drive train for a hybrid vehicle including an engine, a motor having a stator and a rotor, and a transmission receiving driving forces from the engine and the motor, wherein the rotor is supported by an output shaft of the engine and an input member of the transmission.
The rotor preferably has a shaft portion on a rotational center thereof, and the shaft portion of the rotor is supported by the output shaft of the engine, with the shaft portion contacting the output shaft over an axially narrow area.
In a preferred embodiment a recess is formed in an end face of the output shaft of the engine, and a convex portion is formed on an outer surface of the shaft portion of the rotor, wherein the shaft portion of the rotor is inserted into the recess, with the convex portion in contact with a wall surface defining the recess.
The transmission preferably includes a fluid transmission unit having a turbine runner, a pump impeller and a cover, with the cover serving as the input member and being arranged so as to cover the turbine runner and the pump impeller, and the rotor being further supported by a portion of the cover.
The fluid transmission unit preferably has a center piece on a rotational center thereof, and the rotor is centered by the center piece.
A flex plate is preferably arranged between the output shaft of the engine and the rotor to transmit driving force. The flex plate extends to a radially outer side of the stator of the motor, and a sensor detects the extended portion of the flex plate to determine phase of the rotor of the motor.
As shown in FIG. 3, a shaft bushing rotatably supports an end portion of the output shaft of the engine. A recess is formed in the end of the output shaft, and the rotor has a centered rotor shaft inserted into the recess and the rotor is thereby supported by the output shaft, with at least part of the supported shaft portion of the rotor axially overlapping the shaft bushing.
The shaft portion of the rotor is in contact with the output shaft of the engine only over an axially narrow area thereof. Therefore, even if the output shaft rotates eccentrically due to vibrations of the engine, only the contacting position moves and transmission of the eccentric rotation from the output shaft to the shaft of the rotor is minimized.
The rotor is supported by the output shaft via the rotor shaft which is received in the recess of the output shaft. The output shaft is supported by the shaft bushing overlapping with the supported shaft portion of the rotor.
In the invention, the motor is not limited to a motor which converts electrical energy to rotational motion, and may be a generator which converts rotational motion to electrical energy. The engine is a unit which converts fuel combustion energy to rotational motion, and may be a gasoline engine, a diesel engine or the like. The shaft bushing is not limited to a roller bearing, and may be any shaft support, e.g., slide bearing including metal bearing, journal bearing and hydrostatic bearing or the like, oil retaining bearing or gas bearing or the like.
Because the rotor is supported by the output shaft of the engine and the input member of the transmission, a fixed member for rotationally supporting the rotor is not necessary so that the axial dimension and overall size of the drive train can be reduced.
The shaft portion of the rotor is supported by the output shaft of the engine with allowance for movement relative thereto by contact with the output shaft over an axially narrow area thereof. Therefore, the transmission of the vibrations of the engine to the rotor can be reduced. Accordingly, the gap between the rotor and the stator can be reduced so that the efficiency as a motor can be increased.
Because the rotor is supported by the portion of the cover opposed to the rotor on the radially outer side of the cover, the degree of deformation by hydraulic pressure on the radially outer side of the cover is smaller than that in the center portion (the radially inner side). Therefore, even if the cover is deformed by hydraulic pressure, the centering accuracy of the rotor is not compromised.
Because the sensor for detecting the phase of the rotor of the motor is arranged on the radially outer side of the motor and detects the extended portion of the flex plate, the sensor can be sufficiently supported directly by a fixed member, e.g., the motor housing or the like, so that the axial dimension of the gear train can be reduced. Also, in case that the phase of the rotor of the motor is determined by detection of the flex plate, the phase can be detected without providing another member for detection by the sensor.
Because the output shaft is supported by the shaft bushing which is axially overlapped with the supported portion of the rotor, forces acting on the output shaft by supporting the rotor can be directly borne by the shaft bushing so that the affects from the rotor to the output shaft can be reduced.